This invention relates to endoluminal prostheses such as vascular repair devices, and in particular intravascular stents, which are adapted to be implanted into a patient""s body lumen, such as a blood vessel or coronary artery, to maintain the lumen""s patency. Stents are particularly useful in the treatment of atherosclerotic stenosis and are most frequently used in connection with coronary angioplasty.
Stents are tubular, usually cylindrical devices which hold open a segment of blood vessel or other body lumen. They also are suitable to support and hold back a dissected arterial lining that can occlude the lumen. At present, numerous models of stents are marketed throughout the world. While some of these stents are flexible and have the appropriate, strength and rigidity needed to hold open a lumen such as a coronary artery, each stent design nonetheless represents a particular compromise among these properties as well as a number of additional competing parameters. What has been needed, and heretofore unavailable, is a stent which has a higher degree of flexibility both in its crimped as well as expanded state, as well as a reduced crimped profile, a larger expansion range and less unsupported surface area (USA), so that it can more readily be advanced through tortuous lumens and expanded, and yet have the mechanical strength to hold open the lumen or artery into which it is implanted and provide adequate vessel wall coverage.
The present invention provides a stent pattern which simultaneously provides for these advances over previously known stent configurations.
The present invention is directed to an endoluminal prosthesis, such as an intravascular stent, which is highly flexible along its longitudinal axis, both in its crimped state to facilitate delivery through tortuous body lumens as well as in its expanded state to minimize the potential for trauma upon deployment, but which is strong and stable enough radially in its expanded condition to maintain the patency of a body lumen when the stent is implanted therein. Additionally, its low profile while in its crimped state further enhances advanceability while its large expansion range and its minimal unsupported surface area (USA) more effectively provides support upon deployment.
The stent of the present invention includes a plurality of generally cylindrical elements, also known as rings, that are interconnected to form the stent. The stent typically is mounted on a balloon catheter if it is balloon expandable, or else it can be mounted on a catheter without a balloon if it is self-expanding.
Each of the cylindrical rings or elements has a proximal end and a distal end and a cylindrical outer wall surface that extends circumferentially between the proximal end and the distal end of the cylindrical ring. The cylindrical wall is defined by an undulating structure that extends proximally as well as distally. The structure consists of a series of peaks and valleys that are interconnected by bar arms. Undulations of both relatively large amplitude as well as of relatively smaller amplitude are present. In one of the preferred embodiments, the structure alternates between undulations of large amplitude and small amplitude such that each small amplitude undulation is sandwiched between two undulations of large amplitude. In another preferred embodiment, two small amplitude undulations are sandwiched between two undulations of the relatively larger amplitude. In the preferred embodiments at least one of the bar arms extending between an undulation of large amplitude and an undulation of relatively small amplitude is non-linear, preferably having an S-shape. The present invention further provides for the undulations in adjacent cylindrical rings to be either in phase of out of phase. At least one link extends between adjacent rings, wherein such link is preferably non-linear. The link may extend between a valley on one ring and a peak on the adjacent ring. Alternatively, the link may extend between the non-linear bar arm of one ring to the adjacent ring.
The number of peaks, valleys, links, and cylindrical rings can be varied as the application requires. The configuration of the rings and links provides the stent with a high degree of flexibility along the stent axis, both in its crimped state as well as its expanded state. Further, the combination of large and small amplitude undulations along with the non-linear bar arms allows the stent to be crimped to a very small profile while allowing for large expansion and a minimal unsupported surface area upon expansion.
Typically, a balloon expandable stent is made from a stainless steel alloy or similar material. The cylindrical rings of the stent are plastically deformed when expanded by the balloon.
The stent may be formed from a tube by laser cutting the pattern of cylindrical rings and flexible links in the tube. The stent also may be formed by laser cutting a flat metal sheet in the pattern of the cylindrical rings and links, and then rolling the pattern into the shape of the tubular stent and providing a longitudinal weld to form the stent.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the of the invention.